1. Field of the Invention
The present invention relates to a liquid lens to be mounted on mobile phones. In the liquid lens, electrolytes and insulating liquids, of which the curvatures are varied by the application of voltage, are filled in a cylindrical body so as to form a plurality of interfaces in the upper and lower portions thereof by reference to a transmitting partition lens. In this state, as a quantity of electric charge is adjusted through electrodes connected to the electrolytes, an optical zoom function, an auto-focus function, and a minute auto-focus function can be implemented at the same time.
2. Description of the Related Art
In recent years, as new types of mobile terminal, such as mobile phones or personal digital assistances (PDA), integrating a camera have been increasingly released in the market, a demand for a mobile terminal integrating a camera of a high pixel and various functions has been also growing. Such a mobile terminal camera comprises a lens affixed to an image pickup device such as charge coupled device (CCD), complementary metal oxide semiconductor (CMOS), and the like, and is configured to pick up an image of a subject through the lens and to allow data of a picked-up image to be recorded by means of a predetermined recording medium.
In order to provide capability of a mega-pixel level to the camera according to a recent trend, the lens must be designed not only to have sufficient resolving power, but also to have a greater size than those of sensors in consideration of assembly tolerance.
For a lens system mounted to the mobile terminal and used to pick up the image of the subject, it generally suffers from various kinds of aberration, such as spherical aberration, astigmatism, distortion aberration, etc. causing deformation of the shape or the morphology of the image of the subject due to influence of incident light having various wavelengths, which is incident on the lens upon image pickup of the subject. Thus, it is necessary to have implementation which can suppress occurrence of the aberration as much as possible.
Such a lens system can realize zoom in order to have a variable focal length. A zoom function of the lens system can be generally achieved by adjusting a separation between lenses via a relative movement between a front lens having a positive refractive index and a rear lens having a negative refractive index. For a general camera, a wide angle lens or a telephoto lens capable of changing a focal distance between an existing lens and an added lens is additionally affixed to the camera to maximize the zoom function, thereby allowing a user to take a picture at various viewing angles at one place without moving.
The zoom is generally divided into an optical zoom and a digital zoom. The optical zoom refers to a state where the image of the subject is magnified by a variable focal distance by relatively moving an optical lens affixed to the camera. The digital zoom refers to a state where the image of the subject is magnified in the CCD and displayed thereon, as magnifying an image in a graphic program such as Photo-Shop and the like.
For the digital zoom, the image of the subject is magnified in the CCD, thereby allowing elimination of a space for movement of the lenses according to variation in focal distance. As such, the digital zoom is advantageous in terms of miniaturization and compactness, but has a problem in that clear resolution cannot be achieved upon image pickup by the zoom operation.
On the contrary, for the optical zoom, the zoom operation is realized by virtue of the variation in focal distance between the lenses, thereby requiring the space for movement of the lenses according to the variation in focal distance. Hence, the optical zoom is disadvantageous in that it requires a large space for a lens part and a lens barrel surrounding the lens part. However, it can be preferred to the digital zoom by consumers due to its merits in clear resolution upon the zoom operation, irrespective of its disadvantage of increasing the volume of the mobile terminal.
Nevertheless, a recent tendency of miniaturization and compactness in the market requires a decrease in space for changing the focal distance, and thus, manufacturers have mainly released mobile terminals which incorporate the digital zoom function therein rather than the optical zoom function. In recent years, the optical zoom type mobile terminals have also been released, which can embody the optical zoom function through a rear side of the mobile terminal.
Korean Patent Application No. 2003-0003984 discloses one of conventional mobile terminals which can embody the optical zoom function. The mobile terminal of the disclosure has an improved lens barrel structure for an optical zoom applicable to the digital camera and the like. In other words, there are disclosed a lens barrel structure of a zoom camera, which has a small size and high resolution and can be easily manufactured, and a zoom lens assembly with the lens barrel structure.
The zoom lens assembly comprises a front lens, a rear lens having a negative refractive index, an inner barrel which has a helicoid groove formed along a surface of the inner barrel to guide a helical movement of the front and rear lenses, and an outer barrel capable of being inserted along the surface of the inner barrel and having an escaping groove formed on an inner surface of the outer barrel to guide a vertical movement of the front and the rear lenses.
With the zoom camera constructed as above, the inner and outer barrels are positioned at one side of the mobile terminal in a telescopic manner such that a focal distance of the zoom camera can vary in relation to the movement between the lenses as the inner and outer barrels are sequentially spread out by driving of a motor inside the terminal, thereby realizing the optical zoom function. Consequently, the zoom camera of the disclosure has a disadvantage in that it requires a large space for the zoom operation within the camera.
In addition, since the motor of the camera is inevitably operated in such a way so as to push the inner and outer barrels having the plural lenses received therein to an outside of the zoom camera, loss of power during driving of the motor causes an increase in power consumption of a battery.
In order to solve the problems as mentioned above, a liquid lens has been developed, which occupies a small space within the mobile terminal and does not suffer from power consumption. The liquid lens comprises a electrolyte and an insulating liquid in a single lens barrel to form an interface therebetween, of which curvature is changed by application of voltage to the electrolyte through the lens barrel, in order to embody the zoom function.
One of the liquid lenses capable of embodying the zoom function is disclosed in Korean Patent Laid-open Publication No. 2005-0033308, entitled “Zoom camera using the liquid lens for mobile phone, control system and method thereof,” which will be described hereinafter with reference to FIG. 1.
FIG. 1 is a sectional view of a conventional liquid lens. Referring to FIG. 1, the conventional liquid lens includes a first group of lenses 310 comprising a first lens 311 with a positive refractive index and a second lens 312 with a negative refractive index, a first liquid lens 300 comprising an interface formed between a conductive liquid and an insulating liquid, the interface being varied in curvature in response to a control signal for a zoom function, a second group of lenses 330 comprising a third lens 331 having both aspheric surfaces with a positive refractive index and a fourth lens 332 having both aspheric surfaces with a negative refractive index, and an infrared filter 340 spaced at a predetermined distance from the second group of lenses 330.
The conventional liquid lens of the disclosure is operated on the basis of an electrowetting phenomenon, as shown in FIG. 2, wherein the electrowetting phenomenon is caused by variation of the contact angle α resulting from change in surface tension of an interface by movement of charges residing on the interface. In particular, a thin dielectric member is positioned on the interface to allow the interface to have a high potential difference, and the charges in the electrolyte have characteristics of moving towards an upper surface of the interface due to chemical properties.
At this point, when an electric field is applied to the interface from the outside, the characteristics of the charges are further intensified, and the concentration of the charges is significantly increased at a triple contact line where the interfaces overlap each other, thereby increasing repulsive force between the charges. Then, the surface tension is lowered at a corner of a liquid droplet.
Since the electrowetting phenomenon can be used for easy controlling of a minute amount of liquid and fine particles in the liquid, various investigations have been undertaken in recent years for application of the electrowetting phenomenon to a variety of products, for example, liquid lenses, micro pumps, display devices, optical devices, micro electro mechanical systems (MEMS), etc.
In particular, a liquid lens for auto-focus can have improved characteristics in view of small size, low power consumption and rapid response rate, compared with a conventional mechanical driving type lens.
The liquid lens constructed as above can embody the zoom function by virtue of the variation in curvature of the interface between the conductive liquid and the insulating liquid of the individual liquid lens within the single lens barrel in which the plural groups of lenses and the liquid lens are received, thereby solving the problem of spatial restriction by the conventional optical zoom lens which employs the telescopic lens barrel. However, irrespective of these merits, the conventional liquid lens has a problem in that the single liquid lens only permits the zoom function by the variation in curvature between the liquids contained in the barrel.
Further, the conventional liquid lens has a problem of making the structure of the camera complicated. In particular, in order to allow the camera using the liquid lens to embody other functions, for example, an auto-focus (A/F) adjustment function, as well as the zoom function, an additional liquid lens to act as a front lens must be affixed to the camera, making the structure of the camera more complicated.
Furthermore, the insulating liquids and the electrolytes forming a plurality of interfaces are inevitably sensitive to an external impact and swaying, because of a characteristic of the liquid lens. Therefore, although the optical zoom function and the auto-focus function can be embodied with a complicated structure, the auto-focus function for adjusting a focus on an object is not performed in a desired way.